Alteration of annulate lamellae in the in vitro progesterone-treated, full-grown Rana pipiens oocyte.

In full-grown but immature Rana pipiens ovarian oocytes, stacks of annulate lamellae are preferentially localized in the ooplasm between the germinal vesicle and the animal pole.l Furthermore, the largest stacks of these porous cytomembranes tend to be localized deeper in the ooplasm in proximity to the germinal vesicle, while smaller, but variable-sized stacks of annulate lamellae area found closer to the oolemma of the animal pole. Manually defolliculated, full-grown oocytes were cultured in progesterone for periods of 1, 3, 5, 6, 9, 12, 16, 18, and 22 hours at 18 degrees C. Annulate lamellae were observed in the animal pole ooplasm after 1, 3, 5, 6, and 9 hours of in vitro culture in progesterone at 18 degrees C. In contrast, annulate lamellae were not observed in fully grown oocytes cultured in the progesterone for 12, 16, 18, or 22 hours at 18 degrees C. Rather, many localized areas in the animal pole ooplasm wer observed that contained large numbers of closely packed vesicles of different size. The largest clusters of vesicles were present in the ooplasm near the germinal vesicle. Progressing toward the oolemma of the animal pole, the vesicular clusters appeared to become smaller in area. These clusters of vesicles were not observed in either untreated control oocytes at 3-22 hours of culture, or in those treated with progesterone for 1, 3, 5, 6, or 9 hours. The results suggest that after the appropriate maturation-inducing treatment with progesterone, annulate lamellae lose their integrity, probably by a process of vesiculation. This represents one of the first morphological changes which occurs during the induction of meiotic maturation. The alteration of annulate lamellae observed in the progesterone-treated oocytes occurs prior to the complete germinal vesicle breakdown, for under the experimental conditions described, the germinal vesicle nuclear envelope did not completely break down until between 18 and 22 hours of culture in progesterone.